The present invention relates to an irrigation device for plants and, more particularly, to an irrigation device which is automatically activated in correlation with the evapotranspiration needs of the plants.
Many types of devices are known which relieve the necessity of manually watering potted plants. The simplest of these automatic devices deliver a predetermined amount of water to the plant or water the plant for a predetermined amount of time. These devices do not take into account the real-time needs of the plant at the time of watering, but rather work according to a watering rate which was determined previously, at which time the environmental conditions may have been greatly different.
In more sophisticated devices, the watering rate is determined by the current moisture content of the plant and/or its soil. In these devices, the plant is watered only after it has dried out to a specified extent.
One major method of determining the moisture content is to use various moisture sensors placed in the soil or elseware in the vicinity of the plant. These are usually expensive to produce and operate and are not suitable for general use. In a second method, exemplified in U.S. Pat. No. 4,557,071, water is transferred to the soil by capillary action as a function of the dryness of the soil. This method, however, is unreliable as it depends on local soil conditions which may be unrepresentitive. Both of these methods suffer from the major disadvantage that they are not compatible for use with a large number of plants, since each individual plant needs a separate device to control its watering rate.
A third method determines the moisture content of the plant by measuring the weight of the plant together with its soil. This method is disclosed, for example, in U.S. Pat. Nos. 3,168,797, 4,060,934 and 4,760,666. This method also suffers from the forementioned disadvantage that each individual plant requires a separate weighing device. Although U.S. Pat. No. 4,060,934 discloses an automatic water tender which waters a plurality of plants, the controlling mechanism is dependent on the weight loss of a single plant. In the event that the water consumption of the single monitored plant differs from that of the other plants, the other plants will not receive their optimal water portion.